This invention relates to a process for enhancing ethylene yield in microporous solid catalysts used in the conversion of oxygenates to hydrocarbons or olefins. More particularly, this invention relates to a process for enhancing ethylene yields using silicoaluminophosphate molecular sieve catalysts through acid extraction of the catalysts.
Light olefins have traditionally been produced through the process of petroleum cracking. Because of the limited availability and high cost of petroleum sources, the cost of producing light olefins from such petroleum sources has been steadily increasing. Many raise the dire prediction of significant oil shortages in the not-too-distant future. Curtailment in the availability of inexpensive petroleum raw materials threatens the supply of light olefins. Light olefins serve as feeds for the production of numerous chemicals. Ethylene is a light olefin used as a feedstock in many chemical processes.
The search for alternative materials for the production of light olefins or ethylene has led to the use of oxygenates such as alcohols, and more particularly to methanol and ethanol or their derivatives as feedstocks. These and other alcohols may be produced by fermentation or from synthesis gas. Synthesis gas can be produced from natural gas, petroleum liquids, carbonaceous materials including coal, recycled plastics, municipal wastes, or any organic material. Thus, alcohol and alcohol derivatives may provide non-petroleum based routes for hydrocarbon production.
Molecular sieves, such as the crystalline zeolite and silicoaluminophosphate (SAPO) catalysts, are known to promote the conversion of oxygenates to hydrocarbon mixtures. Numerous patents describe this process for various types of molecular sieve catalysts: U.S. Pat. Nos. 3,928,483; 4,025,575; 4,252,479 (Chang, et al.); 4,496,786 (Santilly, et al.); 4,677,243 (Kaiser). However, none of these patents teach or suggest that ethylene yield may be enhanced through treatment of the catalyst with acid.
These and other disadvantages of the prior art are overcome by the present invention, however, and a new improved process for enhancing ethylene yield through the acid treatment of catalysts is provided.